Refactor AssetHandlerRegistry, modernize editor window UI

Refactored AssetHandlerRegistry to a static class and updated all usages. Replaced the docking-based EngineEditorWindow with a new grid/panel layout, adding modern toolbar, menu bar, and status bar. Introduced new divider styles and improved UI details. Removed obsolete and unused files, updated project references, and made minor code and UI/UX improvements.

src/Editor/Ghost.Editor/ActivationHandler.cs

@@ -58,6 +58,8 @@ internal static class ActivationHandler
         {
             ArenaCapacity = 1024 * 1024 * 1024, // 1 GB. Arena using virtual memory, so this is just a reservation and won't actually consume physical memory until used.
             StackCapacity = 1024 * 1024 * 32, // 32 MB. Stack using virtual memory, so this is just a reservation and won't actually consume physical memory until used.
+            FreeListChunkSize = 64 * 1024 * 1024,
+            FreeListDefaultAlignment = 8,
             FreeListConcurrencyLevel = Environment.ProcessorCount
         };